JP2016109732A - Fixing device - Google Patents

Abstract

[PROBLEMS] To improve durability.
A fixing belt 40 has flexibility, and when pressed by a pressure roller 31, a region facing the pressure roller 31 bends to a rotation axis A side. The outer peripheral surface of the end portion of the fixing belt 40 has a region that is separated from the outer peripheral portion 52 when pressed by the pressure roller 31 and a region that is pressed against the outer peripheral portion 52. The lubricant holding portion 57 has a moving range when the outer peripheral surface of the end portion of the fixing belt 40 moves from a position where the fixing belt 40 contacts the outer peripheral portion 52 to a position away from the outer peripheral portion 52 by being pressed by the pressure roller 31. Located in a region including at least a part.
[Selection] Figure 3

Description

  The present invention relates to a fixing device that fixes a toner image formed on a recording medium.

  As a fixing device, for example, a device described in Patent Document 1 is known. The fixing device described in Patent Document 1 includes a pressure roller, a metal sleeve, a fixing member, and a rotation protection cap. The outer peripheral surface of the metal sleeve comes into contact with the pressure roller and is rotated by the pressure roller. The fixing member is disposed inside the metal sleeve and receives a pressing force from the pressure roller via the metal sleeve. The rotation protection cap is disposed at the end of the metal sleeve and rotates with the metal sleeve. In such a fixing device, the recording medium is sandwiched between the pressure roller and the metal sleeve while the pressure roller is pressed against the fixing member.

JP 2002-323821 A

  In the fixing device as described above, the fixing belt (metal sleeve) has flexibility. At the position facing the pressure roller, the fixing belt is bent by the pressure roller so that the outer peripheral surface is recessed inward. When the fixing belt is bent, the end portion of the fixing belt and the belt guide (rotation protection cap) may be rubbed. When the end portion of the fixing belt and the belt guide are rubbed, the fixing belt and / or the belt guide may be worn, and the durability of the fixing device may be reduced.

  SUMMARY An advantage of some aspects of the invention is that it provides a fixing device capable of improving durability of a belt and a belt guide.

  The fixing device of the present invention includes a pressure roller, a fixing belt, a fixing member, and a belt guide. The fixing belt is an endless fixing belt whose outer peripheral surface is in contact with a pressure roller and is driven to rotate by the pressure roller. The fixing member is disposed inside the fixing belt and receives a pressing force from the pressure roller via the fixing belt. The belt guide is disposed at the end of the fixing belt and rotates around the fixing belt. In this fixing device, the recording medium is sandwiched between the pressure roller and the fixing belt while the pressure roller is pressed against the fixing member. The belt guide has a regulating portion, an outer peripheral portion, and a lubricant holding portion. The restricting portion is disposed to face the end portion of the fixing belt and restricts movement of the fixing belt in the rotation axis direction of the belt guide. The outer peripheral portion surrounds the outer peripheral surface of the end portion of the fixing belt and regulates the spread of the fixing belt. The lubricant holding portion is provided on the surface of the regulating portion on the fixing belt side and holds the lubricant. The fixing belt has flexibility, and when pressed by the pressure roller, a region facing the pressure roller is bent toward the rotation shaft. The outer peripheral surface of the end portion of the fixing belt has a region that is separated from the outer peripheral portion when pressed by the pressure roller, and a region that is pressed against the outer peripheral portion. The lubricant holding portion includes at least a part of a moving range when the outer peripheral surface of the end portion of the fixing belt moves from the position in contact with the outer peripheral portion to a position away from the outer peripheral portion by being pressed by the pressure roller. Located in the area.

  In this fixing device, the lubricant holding portion is at least within a moving range when the outer peripheral surface of the end portion of the fixing belt moves from the position in contact with the outer peripheral portion to a position separated from the outer peripheral portion by being pressed by the pressure roller. Located in a region that includes a part. That is, when the fixing belt rotates, the end portion of the fixing belt moves across the lubricant holding portion. As a result, the lubricant held by the lubricant holding portion is forcibly applied to the end portion (end surface) of the moving fixing belt. Since the application of the lubricant is always performed while the fixing belt is rotating, the state in which the lubricant is applied to the end portion of the fixing belt is maintained for a long time. As a result, wear of the fixing belt and / or belt guide is suppressed for a long period of time, and the durability of the fixing device is improved.

  The lubricant holding portion may have a concavo-convex concavo-convex portion provided on the surface on the fixing belt side in the restricting portion. Accordingly, the lubricant is more reliably held by the lubricant entering the concavo-convex portion, so that the lubricant can be applied to the end portion of the fixing belt for a long period of time.

  The uneven portion may have a circular portion and a radial portion. The circular portion may have a concave shape or a convex shape extending in the circumferential direction about the rotation axis. The radial portion may have a concave shape or a convex shape extending in a direction radiating from the rotation axis of the belt guide at a position farther from the rotation axis than the circular portion. The circular portion has a function of holding the lubricant. The radial portion has a function of promoting the application of the lubricant to the end portion of the fixing belt. Thereby, the lubricant holding unit can appropriately apply the lubricant while holding the lubricant for a long period of time.

  The lubricant holding part may have a hollow part. The hollow portion may be formed around the rotation shaft at a position closer to the rotation shaft of the belt guide than the uneven portion. The indented part may be indented from the uneven part toward the rotation axis. As a result, the lubricant that has fallen due to its own weight or the like from a part of the concavo-convex portion located above the recess is held in the recess. In other words, the recessed portion suppresses the lubricant from flowing out from the belt guide. The lubricant held in the dent is supplied again to the concavo-convex portion by dropping due to its own weight, centrifugal force, or the like. Thereby, the lubricant is efficiently used.

  The belt guide may be rotated around the fixing belt by a frictional force between the outer peripheral portion and the fixing belt in a region where the outer peripheral portion and the outer peripheral surface of the end portion of the fixing belt are in contact with each other. Accordingly, rubbing between the outer peripheral portion of the belt guide and the outer peripheral surface of the end portion of the fixing belt is suppressed, so that wear of the fixing belt and / or the belt guide is suppressed.

  The restricting portion may include a butting portion and a separating portion. The abutting portion may be opposed to the end surface of the fixing belt in a state where the outer peripheral surface of the end portion of the fixing belt is in contact with the outer peripheral portion. The spacing portion may be located closer to the rotating shaft than the abutting portion, and may be separated from the fixing belt in the rotating shaft direction relative to the abutting portion. The lubricant holding part may be provided in the separation part. As a result, when the fixing belt is bent toward the rotating shaft side of the belt guide (that is, when the outer peripheral surface of the end portion of the fixing belt moves between a position in contact with the outer peripheral portion and a position away from the outer peripheral portion. ) Is prevented from rubbing the end surface of the fixing belt against the separation portion.

  As for the surface roughness of the abutting portion, Rmax may be 3.2 μm or less and Rsk may be less than 0. As a result, wear between the abutting portion and the end surface of the fixing belt is further suppressed.

  At least one of the abutting part and the outer peripheral part may be formed of a material having higher wear resistance than the spaced part. Since the abutting portion and the outer peripheral portion are in direct contact with the fixing belt, they are more easily worn than other portions of the belt guide. For this reason, with the above configuration, wear at the abutting portion and the outer peripheral portion is suppressed.

  The belt guide may be composed of a resin base material and a filler. The Mohs hardness of the filler may be −1 or less with respect to the Mohs hardness of the strength-holding base material of the fixing belt. Thereby, wear in the belt guide and / or the fixing belt is suppressed.

The inner diameter of the outer peripheral portion may be 25 mm or more and 50 mm or less. The belt guide may have an inertia moment of 2.0 kg · m ² or less on the rotation shaft. Thus, the belt guide is prevented from slipping when the belt guide rotates with the fixing belt.

  The belt guide may have a corner. The corner portion may be formed by connecting the outer peripheral portion and the regulating portion and may face the end surface of the fixing belt. The fixing belt may include a strength holding substrate, an elastic layer that covers the strength holding substrate, and a release layer that covers the elastic layer. The corners may be rounded or rounded. When the corner is rounded, the radius of roundness may be equal to or less than the total length of the elastic layer and the release layer. Or it may be below the length from the outer peripheral surface of a strength maintenance base material to the outer peripheral surface of a mold release layer. Thereby, when the fixing belt is pressed against the corner portion of the belt guide, the elastic layer and the release layer of the fixing belt are elastically deformed, while the deformation of the strength holding base material is suppressed. That is, damage to the fixing belt strength holding substrate is suppressed.

  The inner diameter of the outer peripheral portion may be 25 mm or more and 50 mm or less. The width in which the outer peripheral portion and the outer peripheral surface of the end portion of the fixing belt overlap in the rotation axis direction may be 2.5 mm or more. As a result, a sufficient contact area is ensured between the outer peripheral portion of the belt guide and the outer peripheral surface of the end portion of the fixing belt, so that the belt guide rotates more reliably with respect to the fixing belt.

  The outer peripheral portion may have a tip portion extending toward the fixing belt. The corner on the outer peripheral surface side of the fixing belt at the leading end may be rounded. Thereby, damage to the fixing belt when the fixing belt contacts the corner portion of the belt guide is suppressed.

  According to the present invention, durability can be improved.

1 is a diagram illustrating a schematic configuration of an image forming apparatus including a fixing unit according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the fixing unit in FIG. 1. It is sectional drawing along the III-III line of FIG. It is a front view of a pressure roller. It is an enlarged view of a section around a belt guide. It is a figure which shows the material of a belt guide. It is a perspective view of a section around a belt guide. FIG. 6 is a diagram illustrating an operation of a fixing unit. FIG. 10 is a cross-sectional view of a modification of the fixing unit.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

(Overall configuration of image forming apparatus)
As shown in FIG. 1, the image forming apparatus 1 includes a recording medium transport unit 2, a transfer unit 10, four photosensitive drums 20, four developing units 3, and a fixing unit (fixing device) 30. The

  The recording medium conveyance unit 2 accommodates a sheet P as a recording medium on which an image is finally formed, and conveys the sheet P onto the recording medium conveyance path. The sheets P are stacked and stored in a cassette. The recording medium transport unit 2 causes the paper P to reach the secondary transfer region R at the timing when the toner image transferred to the paper P reaches the secondary transfer region R.

  The transfer unit 10 conveys the toner image formed by the developing unit 3 to the secondary transfer region R where the toner image is secondarily transferred to the paper P. The transfer unit 10 includes a transfer belt 11, suspension rollers 11a, 11b, 11c, and 11d that suspend the transfer belt 11, a primary transfer roller 12 that sandwiches the transfer belt 11 together with the photosensitive drum 20, and a transfer belt together with the suspension roller 11d. 11 and a secondary transfer roller 13 that sandwiches 11.

  The transfer belt 11 is an endless belt that is circulated by suspension rollers 11a, 11b, 11c, and 11d. The primary transfer roller 12 is provided so as to press the photosensitive drum 20 from the inner peripheral side of the transfer belt 11. On the other hand, the secondary transfer roller 13 is provided so as to press the suspension roller 11 d from the outer peripheral side of the transfer belt 11. The transfer unit 10 may further include a belt cleaning device that removes toner attached to the transfer belt 11.

  The photosensitive drum 20 is an electrostatic latent image carrier on which an image is formed on the peripheral surface, and is made of, for example, an OPC (Organic Photo Conductor). The image forming apparatus 1 according to the present embodiment is an apparatus capable of forming a color image. For example, the four photosensitive drums 20 are arranged in the moving direction of the transfer belt 11 corresponding to each color of magenta, yellow, cyan, and black. It is provided along. As shown in FIG. 1, a charging roller 21, an exposure unit 22, a developing unit 3, and a cleaning unit 23 are provided on the circumference of each photoconductive drum 20, respectively.

  The charging roller 21 uniformly charges the surface of the photosensitive drum 20 to a predetermined potential. The exposure unit 22 exposes the surface of the photosensitive drum 20 charged by the charging roller 21 according to an image formed on the paper P. As a result, the potential of the portion of the surface of the photosensitive drum 20 exposed by the exposure unit 22 changes, and an electrostatic latent image is formed. The four developing units 3 develop the electrostatic latent image formed on the photosensitive drum 20 with toner supplied from a toner tank 24 provided corresponding to each developing unit 3, and generate toner images. The four toner tanks 24 are filled with magenta, yellow, cyan, and black toners, respectively.

  The cleaning unit 23 collects toner remaining on the photosensitive drum 20 after the toner image formed on the photosensitive drum 20 is primarily transferred to the transfer belt 11. For example, the cleaning unit 23 may be provided with a cleaning blade and scrape the remaining toner on the photosensitive drum 20 by bringing the cleaning blade into contact with the peripheral surface of the photosensitive drum 20. A neutralizing lamp for resetting the potential of the photosensitive drum 20 may be disposed on the circumference of the photosensitive drum 20 between the cleaning unit 23 and the charging roller 21 in the rotation direction of the photosensitive drum 20.

  The fixing unit 30 attaches and fixes the toner image secondarily transferred from the transfer belt 11 to the paper P to the paper P. The fixing unit 30 includes a pressure roller 31 and a fixing belt 40. The pressure roller 31 is driven by a drive unit 35 (see FIG. 2) and is pressed toward the fixing belt 40 by a pressure mechanism (not shown). The fixing belt 40 is an endless belt having flexibility. Inside the fixing belt 40, a fixing roller (fixing member) 32 (see FIG. 2) is provided. The fixing roller 32 sandwiches the paper P by the pressure roller 31 via the fixing belt 40. The fixing roller 32 is driven and rotated by the pressure roller 31 together with the fixing belt 40. The fixing belt 40 is heated by the heating coil 33 (see FIG. 2). By passing the paper P through a fixing nip portion that is a contact area between the fixing belt 40 and the pressure roller 31, the toner image is melt-fixed on the paper P.

  Further, the image forming apparatus 1 is provided with discharge rollers 4 and 5 for discharging the paper P on which the toner image is fixed by the fixing unit 30 to the outside of the apparatus.

  Next, the operation of the image forming apparatus 1 will be described. When an image signal of an image to be recorded is input to the image forming apparatus 1, the control unit of the image forming apparatus 1 uniformly charges the surface of the photosensitive drum 20 to a predetermined potential by the charging roller 21 based on the received image signal. To charge. Then, the control unit irradiates the surface of the photosensitive drum 20 with laser light by the exposure unit 22 to form an electrostatic latent image.

  On the other hand, in the developing unit 3, the toner and the carrier are adjusted so as to have a desired mixing ratio, and further mixed and agitated to uniformly disperse the toner and adjust the developer to which the optimum charge amount is given. This developer is carried on the developing roller 3a. When the developer is transported to a region facing the photosensitive drum 20 by the rotation of the developing roller 3a, toner in the developer carried on the developing roller 3a is formed on the peripheral surface of the photosensitive drum 20. The electrostatic latent image is developed and the electrostatic latent image is developed. The toner image formed in this manner is primarily transferred from the photosensitive drum 20 to the transfer belt 11 in a region where the photosensitive drum 20 and the transfer belt 11 face each other. On the transfer belt 11, toner images formed on the four photosensitive drums 20 are sequentially stacked to form one stacked toner image. The laminated toner image is secondarily transferred to the paper P conveyed from the recording medium conveyance unit 2 in the secondary transfer region R where the suspension roller 11d and the secondary transfer roller 13 face each other.

  The sheet P on which the laminated toner image is secondarily transferred is conveyed to the fixing unit 30. By passing the paper P between the fixing belt 40 and the pressure roller 31 while applying heat and pressure, the laminated toner image is melt-fixed on the paper P. Thereafter, the paper P is discharged to the outside of the image forming apparatus 1 by the discharge rollers 4 and 5. On the other hand, when the transfer belt 11 includes a belt cleaning device, the toner remaining on the transfer belt 11 may be removed by the belt cleaning device after the laminated toner image is secondarily transferred to the paper P.

(Configuration of fixing unit)
As shown in FIGS. 2 and 3, the fixing unit 30 includes a pressure roller 31, a fixing belt 40, a fixing roller 32, a belt guide 50, and a heating coil 33.

  As shown in FIG. 3, the pressure roller 31 includes a shaft portion 31a and a surface layer portion 31b. The shaft portion 31a is a metal shaft, for example, and is rotatably supported by a support frame (not shown) via ball bearings 34 attached to both ends. The surface layer portion 31b is a heat-resistant elastic layer made of, for example, silicon rubber, and covers the outer peripheral surface of the shaft portion 31a. One end portion of the shaft portion 31 a is connected to the drive unit 35. The pressure roller 31 is rotated by the driving force applied from the driving unit 35. Apart from this, the pressure roller 31 is pressed toward the fixing roller 32 by a pressure mechanism (not shown).

  Here, as shown in FIG. 4, the outer diameter of the pressure roller 31 is formed to satisfy a predetermined condition. Specifically, the length from the center position (D4) to the end position (D1) or position (D7) is set to 1 in the axial direction of the shaft portion 31a. The difference in outer diameter of the pressure roller 31 between the position (D2) and the position (D6) on both sides from the center position (D4) to 0.94 is 0.05 mm (more preferably 0.03 mm) or less. . In addition, the outer diameter difference of the pressure roller 31 between the position (D3) and the position (D5) on both sides from the center position (D4) to 0.63 is 0.05 mm (more preferably 0.03 mm). It is as follows. The contour degree of the outer peripheral surface of the pressure roller 31 is 0.1 mm (more preferably 0.05 mm) or less.

  The fixing belt 40 is a flexible endless belt (a sleeve or a cylindrical belt). As shown in FIG. 5, the fixing belt 40 includes a strength holding base 41, an elastic layer 42, and a release layer 43. The strength holding substrate 41 is made of nickel (Ni), for example, and has a Mohs hardness of 5. The elastic layer 42 is made of, for example, heat-resistant silicone rubber, and covers the outer peripheral surface of the strength holding base material 41. The release layer 43 is formed of, for example, a fluororesin (PFA: tetrafluoroethylene / perfluoroalkoxyethylene copolymer or the like) and covers the outer peripheral surface of the elastic layer 42. The fixing belt 40 is disposed to face the pressure roller 31 so that the axial direction of the fixing belt 40 is the same as the axial direction of the pressure roller 31.

  As shown in FIG. 3, the fixing roller 32 includes a shaft portion 32a, a surface layer portion 32b, and a groove portion 32c (see FIG. 5). The shaft portion 32a is, for example, a metal shaft, and is rotatably supported by a support frame (not shown) via ball bearings 34 attached to both ends. The surface layer portion 32b is a heat-resistant elastic layer made of, for example, silicon rubber, and covers the outer peripheral surface of the shaft portion 32a. The groove portion 32c (see FIG. 5) is a groove formed on the outer peripheral surface of the shaft portion 32a on the surface layer portion 32b side from the position where the ball bearing 34 is attached. The groove portion 32c is formed along the circumferential direction on the outer peripheral surface of the shaft portion 32a. The groove portion 32c faces a bearing portion 54 of the belt guide 50 described later. The groove 32c is filled with a lubricant. The fixing roller 32 is surrounded by the fixing belt 40 (that is, disposed on the inner side of the fixing belt 40), and is disposed so that the axial direction of the shaft portion 32 a is the same as the axial direction of the fixing belt 40. Has been.

  The fixing belt 40 and the fixing roller 32 configured as described above are rotated by being pressed by the pressure roller 31. More specifically, when the pressure roller 31 is pressed against the fixing roller 32, the fixing belt 40 is sandwiched between the pressure roller 31 and the fixing roller 32 (that is, the outer peripheral surface of the fixing belt 40 is The state is in contact with the pressure roller 31). When the pressure roller 31 is driven to rotate in this clamping state, the fixing belt 40 is driven to rotate with respect to the pressure roller 31 by a frictional force with the pressure roller 31. When the paper P is sandwiched between the pressure roller 31 and the fixing belt 40, the fixing belt 40 is driven to rotate through the paper P. The fixing roller 32 is driven and rotated in synchronization with the fixing belt 40 by a frictional force with the fixing belt 40 while receiving the pressing force from the pressure roller 31 via the fixing belt 40.

  As shown in FIG. 3, the belt guide 50 is disposed at each end of the fixing belt 40. The belt guide 50 follows the fixing belt 40 and guides the fixing belt 40. As shown in FIG. 5, the belt guide 50 includes a restriction portion 51, an outer peripheral portion 52, a corner portion 53, and a bearing portion 54.

  The restricting unit 51 restricts the movement of the fixing belt 40 in the direction of the rotation axis A of the belt guide 50. The restricting portion 51 is a disk-shaped plate member having an end portion of the shaft portion 32a of the fixing roller 32 passed through the center portion. The restricting portion 51 is disposed to face the end portion of the fixing belt 40. The detailed configuration of the restricting unit 51 will be described later.

  The outer peripheral portion 52 restricts the spread of the fixing belt 40. The outer peripheral portion 52 is a cylindrical member protruding from the outer peripheral edge of the restricting portion 51 toward the fixing belt 40, and surrounds the outer peripheral surface of the end portion of the fixing belt 40. When the fixing belt 40 is brought close to one belt guide 50, the width L in which the outer peripheral portion 52 of the other belt guide 50 and the outer peripheral surface of the end portion of the fixing belt 40 overlap is 2.5 mm or more in the direction of the rotation axis A ( Room temperature (20 ° C.). The inner diameter of the outer peripheral portion 52 is 25 mm or more and 50 mm or less. The outer peripheral part 52 has a front end part 52a extending to the fixing belt 40 side. A corner 52b on the outer peripheral surface side of the fixing belt 40 at the tip 52a is rounded. The radius of roundness of the corner 52b is, for example, 0.15 mm or more.

  The corner portion 53 is formed by connecting the outer peripheral portion 52 and the restricting portion 51. The corner 53 has a rounded or rounded shape. When the corner portion 53 is rounded, the radius of roundness is equal to or shorter than the total length of the elastic layer 42 and the release layer 43 of the fixing belt 40. In other words, the radius of roundness of the corner 53 is equal to or less than the length from the outer peripheral surface of the strength holding base material 41 to the outer peripheral surface of the release layer 43 in the fixing belt 40.

  The bearing portion 54 is a cylindrical member that protrudes from the inner peripheral edge of the restricting portion 51 to both sides in the direction of the rotation axis A of the belt guide 50. The bearing portion 54 faces the groove portion 32 c so as to surround the groove portion 32 c of the fixing roller 32, and is rotatably supported by the fixing roller 32. In the direction of the rotation axis A, the length of the groove portion 32 c is 20% to 90% of the length of the bearing portion 54. The outer diameter of the groove portion 32 c is 50% to 99% of the inner diameter of the bearing portion 54. A front end portion 54 a on the outer side in the rotation axis A direction of the bearing portion 54 faces the inner ring of the ball bearing 34.

The belt guide 50 having the restriction portion 51, the outer peripheral portion 52, the corner portion 53, and the bearing portion 54 as described above is integrally formed of a resin base material and a filler. As shown in FIG. 6, for example, polyphenylene sulfide resin (PPS) is used as a resin base material, and potassium titanate fiber (K ₂ O · 8TiO ₂ ) is used as a filler. The Mohs hardness of the potassium titanate fiber (filler) is 4, which is −1 or less with respect to the Mohs hardness of nickel (strength holding base material 41). More preferably, for example, polytetrafluoroethylene (PTFE) is used as the resin base material, and mica is used as the filler. The Mohs hardness of mica (filler) is 2 to 3.5, which is -1 or less with respect to the Mohs hardness of nickel (strength holding base material 41).

The belt guide 50 configured as described above rotates with the fixing belt 40. More specifically, as shown in FIG. 2, first, when the fixing belt 40 is pressed by the pressure roller 31, the region of the fixing belt 40 facing the pressure roller 31 is bent toward the rotation axis A side. Mu As a result, the outer peripheral surface of the end portion of the fixing belt 40 has a region spaced from the outer peripheral portion 52 and a region pressed against the outer peripheral portion 52. Among these, in a region pressed against the outer peripheral portion 52, a frictional force is generated between the outer peripheral portion 52 and the fixing belt 40. Due to this frictional force, the belt guide 50 rotates with the fixing belt 40. Here, when the belt guide 50 rotates together with the fixing belt 40 without sliding with respect to the fixing belt 40, and the belt guide 50 rotates together with the fixing belt 40 while slightly slipping. Including the case of The belt guide 50 is configured so that the moment of inertia on the rotation axis A is 2.0 kg · mm ² or less so that the belt guide 50 can easily rotate with the fixing belt 40.

  Next, the restriction part 51 will be described in more detail with reference to FIGS. 5 and 7. As shown in FIGS. 5 and 7, the restricting portion 51 has an abutting portion 55 and a separating portion 56 provided on the surface of the restricting portion 51 on the fixing belt 40 side.

  The end surface of the fixing belt 40 is abutted against the abutting portion 55. The abutting portion 55 is a ring-shaped surface formed inside the outer peripheral edge along the outer peripheral edge of the restricting portion 51. The abutting portion 55 faces the end surface of the fixing belt 40 in a state where the outer peripheral portion 52 is in contact with the outer peripheral surface of the end portion of the fixing belt 40. As shown in FIG. 5, when the fixing belt 40 is brought close to one belt guide 50, the clearance S in the rotation axis A direction between the abutting portion 55 of the other belt guide 50 and the fixing belt 40 is at room temperature. , “(Belt length in the direction of the rotational axis A at 240 ° C.−belt length in the direction of the rotational axis A at room temperature) ÷ 2” or more. The surface roughness of the abutting portion 55 has a maximum height (Rmax) of 3.2 μm or less and a skewness (Rsk) of the roughness curve of less than 0.

  The separating portion 56 is located on the rotation axis A side with respect to the abutting portion 55. The separating portion 56 is separated from the fixing belt 40 along the rotation axis A direction than the abutting portion 55. The spacing part 56 includes a lubricant holding part 57. The lubricant holder 57 holds a lubricant. As the lubricant, for example, a fluorine-based heat resistant grease is used. The lubricant reduces friction between the fixing belt 40 and the belt guide 50.

  The lubricant holding portion 57 has a concavo-convex portion 58 and a recess portion 59. As shown in FIG. 7, the concavo-convex portion 58 is a concavo-convex region, and includes a circular portion 58b and a radial portion 58a. The circular portion 58b is a portion in which a concave shape or a convex shape extends around the rotation axis A along the circumferential direction. In the present embodiment, four ring-shaped concave portions having different diameters are arranged around the rotation axis A, respectively. The radial portion 58a is a portion in which a concave shape or a convex shape extends along a direction radiating from the rotation axis A at a position farther from the rotation axis A than the circular portion 58b. In the present embodiment, elliptical recesses extending along the direction of radiating from the rotation axis A are arranged at predetermined intervals along the circumferential direction of the rotation axis A. The concave portion (or convex portion) of the circular portion 58b and the radial portion 58a has a depth (or height) of 0.05 mm or more and 1.0 mm or less, and the interval between the concave portions (or convex portions). Is 0.2 mm or more and 2.0 mm or less.

The recessed portion 59 is formed around the rotation axis A at a position closer to the rotation axis A of the belt guide 50 than the uneven portion 58. The hollow portion 59 is recessed in a concave shape from the concave-convex portion 58 toward the rotation axis A side. Inner surface of the recessed portion 59 has a 1.0 cm ² or more 4.0 cm ² or less. The recessed portion 59 can hold more lubricant than the uneven portion 58.

  As shown in FIG. 2, the heating coil 33 heats the fixing belt 40 (and the pressure roller 31 via the fixing belt 40). The heating coil 33 has a plate shape curved in an arc shape in cross section. The heating coil 33 is separated from the fixing belt 40 and covers a part of the outer peripheral surface of the fixing belt 40 at a position where the virtual central axis of the heating coil 33 is coaxial with the rotation axis A of the belt guide 50. Note that the region where the fixing belt 40 is pressed against the outer peripheral portion 52 is −40 ° with respect to the angle θ at which the heating coil 33 covers the fixing belt 40 as viewed from the direction of the rotation axis A (the through direction in FIG. 2). That's it.

The heating coil 33 is controlled by a temperature control unit (not shown). As shown in FIG. 4, the temperature control unit uses the temperatures detected by a plurality of (six in this embodiment) temperature sensors TF1 to TF3 and TR1 to TR3 mounted on the pressure roller 31 to perform heating. The coil 33 is controlled. The temperature sensor TF1 measures the surface temperature of the pressure roller 31 at a position that is 0.31 from the position (D4) when the length from the position (D4) to the position (D1) is 1. The temperature sensor TF2 measures the surface temperature of the pressure roller 31 at the position (D3). The temperature sensor TF3 measures the surface temperature of the pressure roller 31 at the position (D2). TR1 measures the surface temperature of the pressure roller 31 at a position that is 0.31 from the position (D4), where the length from the position (D4) to the position (D7) is 1. The temperature sensor TR2 measures the surface temperature of the pressure roller 31 at the position (D5). The temperature sensor TR3 measures the surface temperature of the pressure roller 31 at the position (D6). The temperature control unit controls the heating coil 33 so that T ≦ 0.04 (more preferably 0.02) under the temperature distribution condition shown in the following formula (1). Α indicates the linear expansion coefficient of the pressure roller 31 (surface layer portion 31b), and t indicates the thickness of the pressure roller 31 (surface layer portion 31b).
T = t × 2 × α × (TF1−TR1) ÷ 3 + t × 2 × α × (TF2−TR2) × 2 ÷ 3 + t × 2 × α × (TF3−TR3) (1)

  Next, how the lubricant is supplied to the fixing belt 40 when the fixing unit 30 is operated will be described. As shown in FIG. 8, first, when the paper P is conveyed to the fixing unit 30, the pressure roller 31 is pressed toward the fixing roller 32 and rotated. Accordingly, the fixing roller 32 sandwiches the paper P by the pressure roller 31 via the fixing belt 40. The fixing roller 32 is driven and rotated by the pressure roller 31 together with the fixing belt 40. The outer peripheral surface of the end portion of the fixing belt 40 moves from a position in contact with the outer peripheral portion 52 to a position away from the outer peripheral portion 52 by being pressed by the pressure roller 31 according to the driven rotation.

  More specifically, the area of the fixing belt 40 that is pressed by the pressure roller 31 is released from the state shown in FIG. Across the region B of FIG. At this time, since the lubricant holding portion 57 is included in the region B, the lubricant held by the lubricant holding portion 57 is forcibly applied to the end portion of the fixing belt 40. The application of the lubricant is sequentially performed while the fixing belt 40 is rotated.

  The present embodiment is configured as described above. In the fixing unit 30, the lubricant holding portion 57 is pressed by the pressure roller 31 from the position where the outer peripheral surface of the end portion of the fixing belt 40 contacts the outer peripheral portion 52. It is located in a region including at least a part of the moving range when moving to a position away from the outer peripheral portion 52. That is, when the fixing belt 40 rotates, the end portion of the fixing belt 40 moves so as to cross the lubricant holding portion 57. As a result, the lubricant held by the lubricant holding portion 57 is forcibly applied to the end portion (end surface) of the fixing belt 40 that is moving. Since the application of the lubricant is always performed while the fixing belt 40 is rotating, the state in which the lubricant is applied to the end portion of the fixing belt 40 is maintained for a long time. As a result, the wear of the fixing belt 40 and / or the belt guide 50 is suppressed for a long time, and the durability of the fixing unit 30 is improved.

  The lubricant holding part 57 has a concavo-convex part 58. As a result, since the lubricant is more reliably held by the lubricant entering the concavo-convex portion 58, the lubricant can be applied to the end portion of the fixing belt 40 for a long period of time.

  The uneven portion 58 has a circular portion 58b and a radial portion 58a. The circular portion 58b has a function of holding the lubricant. The radial portion 58a has a function of promoting the application of the lubricant to the end portion of the fixing belt 40. The lubricant holding part 57 having these can be applied appropriately while holding the lubricant for a long period of time.

  The dent 59 is recessed from the concavo-convex part 58 toward the rotation axis A. Accordingly, the lubricant that has fallen due to its own weight or the like from a part of the concavo-convex portion 58 located above the recess 59 is held in the recess 59. That is, the recess 59 suppresses the lubricant from flowing out from the belt guide 50 to the outside. The lubricant held in the depression 59 is supplied again to the concavo-convex portion 58 by dropping due to its own weight, centrifugal force, or the like. Thereby, the lubricant is efficiently used.

  The belt guide 50 is rotated around the fixing belt 40 by a frictional force between the outer peripheral portion 52 and the fixing belt 40 in a region where the outer peripheral portion 52 and the outer peripheral surface of the end portion of the fixing belt 40 are in contact with each other. . As a result, rubbing between the outer peripheral portion 52 of the belt guide 50 and the outer peripheral surface of the end portion of the fixing belt 40 is suppressed, so that wear of the fixing belt 40 and / or the belt guide 50 is suppressed.

  The spacing portion 56 is located on the rotation axis A side with respect to the abutting portion 55 and is separated from the fixing belt 40 in the direction of the rotation axis A with respect to the abutting portion 55. Thus, when the fixing belt 40 is bent toward the rotation axis A of the belt guide 50 (that is, the position where the outer peripheral surface of the end portion of the fixing belt 40 is in contact with the outer peripheral portion 52 and the position where the outer peripheral portion 52 is separated from the outer peripheral portion 52). The end face of the fixing belt 40 is prevented from rubbing against the separating portion 56 when the head is moved between the two.

  The surface roughness of the abutting portion 55 is such that Rmax is 3.2 μm or less and Rsk is less than zero. Thereby, the wear between the abutting portion 55 and the end face of the fixing belt 40 is further suppressed. Further, even when the abutting portion 55 and the end surface of the fixing belt 40 are rubbed, generation of noise (sound when rubbed) is suppressed.

  The belt guide 50 is composed of a resin base material and a filler. The Mohs hardness of the filler is −1 or less with respect to the Mohs hardness of the strength holding base material 41. Thereby, wear in the belt guide 50 and / or the fixing belt 40 is suppressed. As a comparative example, FIG. 6 shows a case where PPS is used for the resin base material and glass fiber (GF) is used for the filler. The Mohs hardness of GF (filler) is 5 to 6.5. In this case, the Mohs hardness of GF (filler) is −1 or more than the Mohs hardness of nickel (strength-holding base material 41), so that the fixing belt 40 is greatly worn.

The belt guide 50 has an inertia moment on the rotation axis A of 2.0 kg · m ² or less. As a result, the belt guide 50 is prevented from slipping when the belt guide 50 rotates around the fixing belt 40.

  The radius of roundness of the corner 53 is equal to or shorter than the total length of the elastic layer 42 and the release layer 43. In other words, the length is less than or equal to the length from the outer peripheral surface of the strength-holding base material 41 to the outer peripheral surface of the release layer 43, and the most desirable is a square shape with a rounded radius of zero. Thus, when the fixing belt 40 is pressed against the corner 53 of the belt guide 50, the elastic layer 42 and the release layer 43 of the fixing belt 40 are elastically deformed, while the deformation of the strength holding base material 41 is suppressed. . That is, damage to the strength holding substrate 41 of the fixing belt 40 is suppressed.

  A width in which the outer peripheral portion 52 and the outer peripheral surface of the end portion of the fixing belt 40 overlap in the direction of the rotation axis A is 2.5 mm or more. As a result, a sufficient contact area is secured between the outer peripheral portion 52 of the belt guide 50 and the outer peripheral surface of the end portion of the fixing belt 40, so that the belt guide 50 rotates more reliably with respect to the fixing belt 40. .

  A corner 52b on the outer peripheral surface side of the fixing belt 40 at the tip 52a is rounded. Thereby, damage to the fixing belt 40 when the fixing belt 40 contacts the corner portion 52b of the belt guide 50 is suppressed.

  In the heating coil 33, the virtual central axis of the heating coil 33 is coaxial with the rotation axis A of the belt guide 50. Thereby, variation in the distance (gap) from the heating coil 33 to the fixing belt 40 is suppressed. As a result, the heating to the fixing belt by the heating coil 33 is homogenized, and the temperature unevenness of the fixing belt 40 is reduced. The angle of the region where the outer peripheral surface of the end portion of the fixing belt 40 is pressed against the outer peripheral portion 52 is −40 ° or more with respect to the angle θ where the heating coil 33 covers the fixing belt 40. As a result, a sufficient heating area of the fixing belt 40 is ensured, so that the heating state of the fixing belt 40 is stabilized.

  The difference in outer diameter of the pressure roller 31 between the position (D2) and the position (D6) on both sides from the center position (D4) to 0.94 is 0.05 mm (more preferably 0.03 mm) or less. . In addition, the outer diameter difference of the pressure roller 31 between the position (D3) and the position (D5) on both sides from the center position (D4) to 0.63 is 0.05 mm (more preferably 0.03 mm). It is as follows. The contour degree of the outer peripheral surface of the pressure roller 31 is 0.1 mm (more preferably 0.05 mm) or less. Accordingly, it is possible to suppress the axial deviation of the shaft portion 31a of the fixing belt 40 due to the difference in outer diameter to the one side. As a result, the occurrence of buckling or the like in the fixing belt 40 can be suppressed. Further, the durability of the fixing belt can be improved.

  A temperature control unit (not shown) controls the heating coil 33 so that T ≦ 0.04 (more preferably 0.02) in Equation (1). Thereby, even if the diameter of the pressure roller 31 changes due to thermal expansion, the difference in outer diameter in the axial direction of the shaft portion 31a can be kept within a slight difference range. As a result, it is possible to suppress the axial deviation of the shaft portion 31a of the fixing belt 40 due to the difference in outer diameter to one side.

  The bearing portion 54 faces the groove portion 32 c so as to surround the groove portion 32 c of the fixing roller 32. Thus, the contact area between the belt guide 50 and the fixing roller 32 is reduced by making the bearing portion 54 and the groove portion 32c face each other. Moreover, the groove part 32c can hold | maintain a lubricant. As a result, the belt guide 50 can rotate more smoothly.

  The tip 54 a on the outer side in the direction of the rotation axis A faces the inner ring of the ball bearing 34. Accordingly, the movement of the belt guide 50 in the direction of the rotation axis A is restricted by the front end portion 54 a abutting against the ball bearing 34. Further, since the inner ring of the ball bearing 34 rotates in synchronization with the fixing roller 32, it is difficult to prevent the belt guide 50 from rotating.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

  In the above embodiment, the restricting portion 51 (the abutting portion 55 and the separating portion 56), the outer peripheral portion 52, the corner portion 53, and the bearing portion 54 are integrally formed. At least one of the portions 52 may be formed of a material having higher wear resistance than the spacing portion 56. The abutting portion 55 and the outer peripheral portion 52 are more easily worn than the other portions of the belt guide 50 because the fixing belt 40 is in direct contact. For this reason, with the above configuration, wear at the abutting portion 55 and the outer peripheral portion 52 is suppressed. In addition, for example, a rigid heat-resistant material can be used in the belt guide 50 other than the abutting portion 55 and the outer peripheral portion 52. Thereby, even when a force is applied to the belt guide 50 from the fixing belt 40 or when heat is transmitted from the fixing belt 40 heated by the heating coil 33, the component accuracy in the belt guide 50 is ensured. The

  In the above embodiment, only the heating coil 33 heats the fixing belt 40. However, as shown in FIG. 9, two auxiliary heating coils 133 may be provided in addition to the heating coil 33. . In this case, the two auxiliary heating coils 133 are arranged on both sides of the heating coil 33 in the direction of the rotation axis A, and are controlled by a temperature control unit (not shown). Such a configuration is effective when the end of the pressure roller 31 is not easily heated. By using the auxiliary heating coil 133 in addition to the heating coil 33, the temperature distribution condition shown in the above formula (1) can be easily satisfied. Note that the auxiliary heating coil 133 may be disposed only on one side of the heating coil 33 in accordance with the structural characteristics of the fixing unit 30. For example, when the fixing belt 40 tends to be close to one end of the pressure roller 31 (the outer diameter of one end of the pressure roller 31 is large), the auxiliary heating coil 133 has an outer diameter of the pressure roller 31. It may be arranged on the smaller side. In this case, one end portion of the pressure roller 31 is heated by the auxiliary heating coil 133, so that the outer diameter of the one end portion of the pressure roller 31 is increased due to thermal expansion. Thereby, it is possible to prevent the fixing belt 40 from being shifted to one side.

  The auxiliary heating coil 133 generates heat when electricity is passed through the coil. However, the present invention is not limited to this, and a heat source such as a lamp may be used instead of the auxiliary heating coil 133. Further, the heating source is not limited, and a cooling source for cooling the pressure roller 31 or the like may be used instead of the auxiliary heating coil 133.

  A position detection sensor that directly detects the position of the fixing belt 40 in the direction of the rotation axis A may be provided. In this case, instead of controlling the heating coil 33 and the like under the temperature distribution condition shown in the above formula (1), the temperature control unit changes the heating coil 33 and the like according to the deviation of the fixing belt 40 detected by the position detection sensor. You may control. Specifically, when the fixing belt 40 is close to one end of the pressure roller 31, for example, the heating coil 33 and / or the auxiliary heating coil 133 is on the side opposite to the side where the fixing belt 40 is close. The amount of heat generated can be increased. Accordingly, the deviation of the fixing belt 40 toward one side can be controlled based on the detection result of the position detection sensor.

  In the above embodiment, the image forming apparatus 1 includes the rotatable fixing roller 32 as a fixing member that receives the pressing force from the pressure roller 31. However, instead of the fixing roller 32, the image forming apparatus 1 includes a non-rotating fixing member. May be. The tandem image forming apparatus 1 shown in FIG. 1 is an example of an image forming apparatus using the fixing unit 30 according to the present embodiment, and the fixing unit 30 according to the present embodiment can use various types of image forming apparatuses. It can be applied to a forming apparatus. Further, as the image forming apparatus, for example, a printer, a FAX, a copying machine, or the like can be used.

  DESCRIPTION OF SYMBOLS 30 ... Fixing unit (fixing apparatus), 31 ... Pressure roller, 32 ... Fixing roller (fixing member), 40 ... Fixing belt, 41 ... Strength retention base material, 42 ... Elastic layer, 43 ... Release layer, 50 ... Belt Guide, 51 ... Restriction part, 52 ... Outer peripheral part, 52a ... Tip part, 52b ... Corner part, 53 ... Corner part, 55 ... Abutting part, 56 ... Separating part, 57 ... Lubricant holding part, 58 ... Uneven part, 58a ... Radial part, 58b ... Circular part, 59 ... Indentation part.

Claims (13)

A pressure roller;
An endless fixing belt whose outer peripheral surface is in contact with the pressure roller and is driven to rotate by the pressure roller;
A fixing member disposed inside the fixing belt and receiving a pressing force from the pressure roller via the fixing belt;
A belt guide disposed at an end of the fixing belt and rotated around the fixing belt;
A fixing device for sandwiching a recording medium between the pressure roller and the fixing belt in a state where the pressure roller is pressed against the fixing member;
The belt guide is
A restricting portion that is disposed to face an end portion of the fixing belt and restricts movement of the fixing belt in a rotation axis direction of the belt guide;
An outer peripheral portion that surrounds an outer peripheral surface of an end portion of the fixing belt and restricts the spread of the fixing belt;
A lubricant holding part that is provided on the surface of the fixing belt in the restricting part and holds a lubricant;
The fixing belt has flexibility, and when pressed by the pressure roller, a region facing the pressure roller is bent toward the rotating shaft,
The outer peripheral surface of the end portion of the fixing belt has a region that is separated from the outer peripheral portion by being pressed by the pressure roller, and a region that is pressed against the outer peripheral portion,
The lubricant holding portion has a movement range when the outer peripheral surface of the end portion of the fixing belt moves from a position in contact with the outer peripheral portion to a position separated from the outer peripheral portion by being pressed by the pressure roller. A fixing device located in an area including at least a part.   The fixing device according to claim 1, wherein the lubricant holding portion includes a concavo-convex concavo-convex portion provided on a surface on the fixing belt side of the regulating portion.   The uneven portion radiates from the rotation shaft of the belt guide at a position farther from the rotation shaft than the circular portion, and a circular portion having a concave shape or a convex shape extending in the circumferential direction around the rotation shaft. The fixing device according to claim 2, further comprising: a concave portion or a radial portion having a convex shape extending along the direction of the fixing. The lubricant holding portion has a recess formed around the rotation shaft at a position closer to the rotation shaft of the belt guide than the uneven portion,
The fixing device according to claim 2, wherein the recessed portion is recessed from the uneven portion toward the rotating shaft.   The belt guide rotates with the fixing belt by a frictional force between the outer peripheral portion and the fixing belt in a region where the outer peripheral portion and the outer peripheral surface of the end portion of the fixing belt are in contact with each other. Item 5. The fixing device according to any one of Items 1 to 4. The regulation part is
In a state where the outer peripheral surface of the end portion of the fixing belt is in contact with the outer peripheral portion, an abutting portion facing the end surface of the fixing belt;
A separation portion located on the rotating shaft side with respect to the abutting portion, and
The spacing portion is spaced from the fixing belt along the rotation axis direction than the abutting portion,
The fixing device according to claim 1, wherein the lubricant holding portion is provided in the separation portion.   The fixing device according to claim 6, wherein the surface roughness of the abutting portion has a maximum height (Rmax) of 3.2 μm or less and a skewness (Rsk) of a roughness curve of less than 0.   8. The fixing device according to claim 6, wherein at least one of the abutting portion and the outer peripheral portion is formed of a material having higher wear resistance than the separation portion. The belt guide is composed of a resin base material and a filler,
The fixing device according to claim 1, wherein a Mohs hardness of the filler is −1 or less with respect to a Mohs hardness of a strength-holding base material of the fixing belt. The inner diameter of the outer peripheral portion is 25 mm or more and 50 mm or less,
The fixing device according to claim 1, wherein the belt guide has an inertia moment of 2.0 kg · mm ² or less on the rotation shaft. The belt guide is formed by connecting the outer peripheral portion and the restricting portion, and has a corner portion facing an end surface of the fixing belt,
The fixing belt has a strength holding base, an elastic layer covering the strength holding base, and a release layer covering the elastic layer,
The corner is rounded or rounded with no roundness,
The radius of roundness when the corner is rounded is equal to or less than the total length of the elastic layer and the release layer, or from the outer peripheral surface of the strength-holding substrate. The fixing device according to claim 1, wherein the fixing device has a length equal to or shorter than the length to the outer peripheral surface of the release layer. The inner diameter of the outer peripheral portion is 25 mm or more and 50 mm or less,
The fixing device according to claim 1, wherein a width in which the outer peripheral portion and an outer peripheral surface of the end portion of the fixing belt overlap in the rotation axis direction is 2.5 mm or more. The outer peripheral portion has a tip portion extending toward the fixing belt,
The fixing device according to claim 1, wherein a corner portion of the fixing belt at the front end portion is rounded.

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